A series of optical devices is used to direct the incident light, reflected light, and fluorescence to detectors. A beam-shaping lens is used to focus the laser down to a nar- row beam waist of 20 to 100 um in the sensing area. In mul ticolor analysis, separation of multicolored light is accom- plished by the combined use of filters and dichroic mirrors. A short-pass filter allows only light of short wavelengths to pass and blocks that of the longer wavelengths. A long-pass filter acts the opposite way. Dichroic mirrors, in contrast, allow light of certain wavelengths to pass and reflect the light that is not allowed to pass.